At home, when I'm on the computer, I usually listed to Chronix Radio (www.chronixradio.com) via iTunes. At work, which won't let us use iTunes and blocks Chronix Radio, I listed to my own MP3s. Most common bands I usually listen too: Tool, Killswitch Engage, Metallica, Distrubed, etc.
Sometimes I'll get in a techno/electronic mood and will listen to Paul Oakenfold, Crystal Method, John Digweed, etc. Then, there are those odd days when I'll listen to Eminem or Dr.Dre.